Despite the tremendous clinical significance of the diseases caused by the five human herpes viruses, little is known about immunity to these viruses. Recent studies with HSV-1, however, have indicated that the primary inducers and targets of humoral and cell-mediated immunity are the viral glycoproteins. The availability of HSV-1 mutants unable to synthesize one or more viral glycoproteins would afford a unique opportunity to examine the role of each glycoprotein in the immune response to this virus. Moreover, mutants exhibiting specific defects in glycoprotein synthesis would constitute invaluable tools for dissecting the stages in HSV-1 glycoprotein synthesis, maturation and expression. We propose, therefore, to isolate and characterize glycoprotein-deficient mutants of HSV-1. For mutant isolation, wild-type virus and cloned wild-type viral DNA fragments encoding the structural genes for viral glycoproteins will be mutagenized. Mutations in mutagenized fragments will be transferred to the wild-type virus genome by co-transfection of cells with mutagenized fragments and wild-type viral DNA. Mutants will be selected by immune cytolysis mediated either by glycoprotein-specific antisera and complement or by lymphocytes immune to specific glycoproteins. This procedure has already resulted in the isolation of mutants which exhibit altered synthesis and/or expression of three of the five major HSV-1 glycoproteins. Mutants with altered specificity in neutralization tests will also be sought using monoclonal antibodies. Following their isolation, mutants will be characterized immunologically and biochemically. Immunologic characterization will include tests of the ability of mutant-infected cells to serve as inducers and targets of humoral and cell-mediated immunity. Mutant glycoproteins and glycoprotein precursors will be characterized biochemically with regard to synthesis, maturation and expression at the cell surface. Collectively, these studies should serve to expand current knowledge of 1) the roles of individual viral glycoproteins in the induction of immunity to HSV, and 2) glycoprotein processing in HSV-infected cells.